Microwave applicator

ABSTRACT

A microwave applicator is disclosed employing a ring resonator. The ring resonator is excited such that traveling electromagnetic wave energy repetitively circulates around the ring. The ring resonator is apertured for passage of material to be treated through the ring resonator for treatment by the traveling wave energy therein. In one embodiment the ring resonator is apertured in diametrically opposed regions of the closed loop such that a sheet of material to be treated is subjected to two treatments by the traveling wave energy in one passage through the resonator. In another embodiment, a non-reciprocal directional coupler is employed for exciting the traveling wave energy within the ring resonator.

United States Patent 1 Aine [ 5 1 Jan. 9, 1973 '[76] Inventor:

[54] MICROWAVE APPLICATOR Harry E. Aine, 2500 El Camino Real, Palo Alto, Calif. 94306 221 Filed: May25, 1971 21 Appl.No.: 146,731

Primary ExaminerJ. V. Truhe Assistant Examiner-Hugh D. Jaeger Attorney-Harry E. Aine and William J. Nolan HIGH FREQUENCY SOURCE 57 I ABSTRACT A microwave applicator is disclosed employing a ring resonator. The ring resonator is excited such that traveling electromagnetic wave energy repetitively circulates around the ring. The ring resonator is apertured for passage of material to be treated through the ring resonator for treatment by the traveling wave energy therein. In one embodiment the ring resonator is apertured in diametrically opposed regions of the closed loop such that a sheet of material to be treated is subjected to two treatments by the traveling wave energy in one passage through the resonator. In another embodiment, a non-reciprocal directional coupler is employed for exciting the traveling wave energy within the ring resonator.

9 Claims, 3 Drawing Figures 4 E OR H PLANE I DIRECTIONAL COUPLER TERMINATION MICROWAVE APPLICATOR DESCRIPTION OF THE PRIOR ART Heretofore, thin sheets of dielectric material have been treated with microwave energy by feeding the sheets through a multi-mode cavity resonator excited with microwave energy. The multi-mode cavity resonator is arranged such that the electric field vector of the standing wave pattern established within the multimode cavity is generally in the plane of the sheet material to-be treated, whereby efficient use of the electric field for treatment of the sheet material is obtained.

However, one of the problems with a multi-mode cavity resonator applicator is that the standing wave pattern is discontinuous in the sense that the intense regions of electric field are concentrated in a certain pattern corresponding to the standing wave pattern established within the resonator. This produces a nonuniform application of the electric field over the surface of the sheet being treated. Attempts have been made to stagger the positions of the intense standing wave electric field patterns within the resonator to obtain a more uniform application of the electric field to the sheet. However, staggering of the standing wave pattern has not been entirely satisfactory.

Others have attempted to obtain a uniform application of microwave energy to sheets of material by passing the sheet material through a waveguide with the plane of the sheet being parallel to the electric field vector within the waveguide and disposed in the region of the most intense field within the guide. Generally, this means that the plane of the sheet passes through the waveguide centrally thereof and parallel to the narrow sides of the rectangular waveguide. In order to prevent standing wave patterns from developing within the waveguide, the end of the guide remote from the source is terminated in a non-reflective resistive load. While this type of microwave applicator avoids the standing wave patterns, it results in inefficient application of the microwave energy to the sheet being treated, particularly in the case of treatment of low loss dielectric sheets, where a large portion of the microwave energy is dumped into the non-reflective termination.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved applicator for applying high frequency electromagnetic wave energy to a material to be treated. 7

One feature of the present invention is the provision of a high frequency electromagnetic wave energy applicator employing a ring resonator excited with high frequency electromagnetic waveenergy for applying the high frequency energy to the material to be treated.

In another feature of the present invention, a high frequency electromagnetic wave energy applicator includes a ring resonator to provide a closed path for the flow of wave energy therearound, and wherein the ring resonator is excited with a traveling wave which circulates repetitively around the closed path, and wherein the material to be treated is exposed within the ring resonator to the traveling wave, whereby uniform treatment of the material is obtained.

In another feature of the present invention, a microwave applicator includes a hollow, rectangular waveguide having a pair of mutually opposed broad' walls interconnected by a pair of mutually opposed narrow side walls and at least one of the broad walls being" centrally apertured for passing the material therethrough into the ring resonator for treatment by the electromagnetic field therein.

In another feature of the present invention, a ring resonator is apertured in diametrically opposed regions of its closed wave path, and means are provided for passing the material to be treated through the diametrically apertured portions of the ring resonator, whereby the material is subjected twice to the treating wave energy in one pass through the applicator.

In another feature of the present invention, a traveling wave ring resonator applicator is excited by means of a non-reciprocal, directional coupler, whereby improved control over the excitation of the wave energy within the ring resonator is obtained.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic line diagram, partly in block diagram form, ofa microwave applicator incorporating features of the present invention,

FIG. 2 is an enlarged sectional view of a portion of the structure of FIG. I taken along line 2-2 in the direction of the arrows and modified to include a material feed and take'up means, and

FIG. 3 is a diagram similar to that of FIG. I depicting an alternative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, there is shown a microwave applicator l incorporating features of the present invention. The applicator 1 includes a ring resonator 2 generally of the type disclosed in articles entitled, Resonance Properties of Ring Circuits: and Resonant Properties of Non-Reciprocal Ring Circuits, appearing in the IRE Transactions of Microwave Theory and Technique, of January, 1957 and 1958, respectively, pages 5156 and 66-71, respectively.

A high frequency source 3, such as a magnetron or klystron oscillator is coupled to the ring resonator 2 via the intermediary of a directional coupler 4. The directional coupler 4 includes a resistive termination 5 and may couple to either the E or H plane of the ring resonator 2.

High frequency wave energy at the resonator frequency of the ring resonator 2 is directionally coupled into the ring resonator 2 for exciting a traveling wave at the resonant frequency of the ring resonator 2 which repetitively circulates around the ring resonator l in one direction, which for the purposes of explanation will be taken as the counterclockwise direction.

In a typical example, the ring resonator structure 2 comprises a length of rectangular waveguide which has the ends connected together to form a ring. The rectangular waveguide includes a pair of mutually opposed broad walls 6 interconnected by a pair of narrow side walls 7. The broad walls 6 are centrally apertured with a slot 8 running lengthwise of each of the broad walls 6. The ring resonator structure 2 is preferably slotted 8 in diametrically opposed regions 9 and 11 such that a sheet of insulative material 12 to be treated, as supplied from a supply roll 13, is drawn through the diametrically opposed slotted regions 9 and l l for treatment by the electric field within the ring resonator and taken up on a take-up roll 14.

The advantage to the ring resonator applicator l is that the sheet of material 12 is disposed in a region of intense uniform electric field such that the sheet receives uniform treatment across the entire width thereof. Moreover, use of the ring resonator allows a relatively low power source 3 to be employed for exciting the resonator 2 as the resonator 2 provides a power amplification in the ring dependent upon the Q of the ring resonator 2. Thus, the advantages ofa resonant applicator are obtained without the disadvantages of the attendant non-uniformity in the electric field obtained by the prior art standing wave applicator.

Another advantage to passing the sheet through diametrically opposed regions of the resonator 2 is that any non-uniformity in the absorption of wave energy taken from one side edge of the sheet 12 to the other side edge, in the first treatment region 9, is compensated by causing the wave energy to pass in the opposite direction across the sheet in the second treatment reg-ion 11.

Referring now to FIG. 3, there is shown an alternative microwave applicator l incorporating features of the present invention. Applicator 15 of FIG. 3 is substantially the same as that previously described with regard to F168. 1 and 2 with the exception that a nonreciprocal directional coupler 16 is employed instead of the directional coupler 4 of FlG. 1. Ring resonators excited by means of a non-reciprocal directional coupler 16 are described in the literature. For example, see an article entitled Non-Reciprocal Directional Couplers appearing in the lRE Transactions on Microwave Theory and Technique, July 1965 issue, pages 474-475, and a research report PlBMRI-l 110- 63 titled, The General Theory Of Non-Reciprocal Directional Couplers and Application in TWR Circuits, published by the Polytechnic Institute of Brooklyn, N.Y., March, 1963, authored by H. Berger. A non-reciprocal directional coupler 16 is a lossless non-reciprocal matched four port network (circulator or bridge) with two distinct pairs of uncoupled ports.

The advantage to the use of the non-reciprocal directional coupler 16 in a resonant ring applicator 15 is that improved isolation is obtained between the high frequency source 3 and the amplified wave energy traveling around within the ring resonator 2. Also such non-reciprocal directional coupler 16 allows improved adjustment of the coupling betweenthe source 3 and the forward traveling wave within the ring 2. Separate adjustment of the backward coupling coefficient also allows improved isolation between the termination 5 and the loop 2.

Although in a preferred embodiment, the ring resonator 2 has been described above as a length of dominant mode rectangular waveguide, other hollow waveguide cross sections may be employed. For example, circular cross section waveguide. Also the material to be treated need not pass in a direction transverse to the direction of power flow in the guide but may pass in the direction of power flow in the guide. The material to be treated need not be sheet form but may be carried on an insulative belt or web that may have a plane in the direction of the E field or perpendicular to the E field. If a conductive belt or web carrier is employed it may extend across the guide with the plane of the belt or web perpendicular to the E vector. Fluid or granular material to be treated may drop or flow through the waveguide.

What is claimed is: I

1. In a high frequency electromagnetic applicator for treating materials with high frequency electromagnetic wave energy, traveling wave ring resonator means for providing a closed circuit loop wave supportive path, means for exciting said ring resonator means with a unidirectional traveling electromagnetic wave that circulates repetitively around said closed circuit path, and means for passing a material to be treated with electromagnetic wave energy through at least a portion of said ring resonator for treating said material with electromagnetic wave energy within said excited ring resonator means.

2. The apparatus of claim '1 wherein said ring resonator means includes, a hollow waveguide arranged in a closed circuit loop to provide said closed path for flow of wave energy therearound.

3. The apparatus of claim 2 wherein said hollow waveguide is of rectangular cross section having a pair of mutually opposed broad walls interconnected by a pair of mutually opposed-narrow side walls, at least one of said broad walls being centrally apertured, and wherein said means for passing material through at least a portion of said ring resonator includes means for passing material through said centrally apertured broad wall of said waveguide.

4. The apparatus of claim 3 wherein said central aperture in said broad wall includes a slot elongated in the direction of the power flow along said rectangular waveguide, and wherein said material to be treated comprises material in sheet form, and wherein said means for passing the material through said apertured broad wall includes means for passing said sheet material through said slotted broad wall of said waveguide. Y

5. The apparatus of claim 2 wherein said ring resona tor is apertured in diametrically opposed regions of said closed path of said ring resonator, and wherein said means for passing the material to be treated through said resonator includes, means, for passing the material to be treated through said diametrically apertured re gions of said closed path, whereby said material is twice subjected to the treating wave energy in one pass through the applicator.

6. The apparatus of claim 2 wherein said means for exciting atraveling wave in said ring resonator includes directional coupler means.

7. The apparatus of claim 6 wherein said directional coupler means is a non-reciprocal directional coupler means.

8. A method for treating materials with high frequency electromagnetic wave energy including the steps of, exciting a traveling wave ring resonator with a treated is a dielectric sheet, and wherein the sheet is passed through said resonator with the plane of the sheet substantially parallel to the electric field vector of the traveling wave energy within the resonator. 

1. In a high frequency electromagnetic applicator for treating materials with high frequency electromagnetic wave energy, traveling wave ring resonator means for providing a closed circuit loop wave supportive path, means for exciting said ring resonator means with a unidirectional traveling electromagnetic wave that circulates repetitively around said closed circuit path, and mEans for passing a material to be treated with electromagnetic wave energy through at least a portion of said ring resonator for treating said material with electromagnetic wave energy within said excited ring resonator means.
 2. The apparatus of claim 1 wherein said ring resonator means includes, a hollow waveguide arranged in a closed circuit loop to provide said closed path for flow of wave energy therearound.
 3. The apparatus of claim 2 wherein said hollow waveguide is of rectangular cross section having a pair of mutually opposed broad walls interconnected by a pair of mutually opposed narrow side walls, at least one of said broad walls being centrally apertured, and wherein said means for passing material through at least a portion of said ring resonator includes means for passing material through said centrally apertured broad wall of said waveguide.
 4. The apparatus of claim 3 wherein said central aperture in said broad wall includes a slot elongated in the direction of the power flow along said rectangular waveguide, and wherein said material to be treated comprises material in sheet form, and wherein said means for passing the material through said apertured broad wall includes means for passing said sheet material through said slotted broad wall of said waveguide.
 5. The apparatus of claim 2 wherein said ring resonator is apertured in diametrically opposed regions of said closed path of said ring resonator, and wherein said means for passing the material to be treated through said resonator includes, means for passing the material to be treated through said diametrically apertured regions of said closed path, whereby said material is twice subjected to the treating wave energy in one pass through the applicator.
 6. The apparatus of claim 2 wherein said means for exciting a traveling wave in said ring resonator includes directional coupler means.
 7. The apparatus of claim 6 wherein said directional coupler means is a non-reciprocal directional coupler means.
 8. A method for treating materials with high frequency electromagnetic wave energy including the steps of, exciting a traveling wave ring resonator with a unidirectional traveling electromagnetic wave, and passing the material to be treated through at least a portion of said ring resonator for treating said material with electromagnetic wave energy within the excited traveling wave ring resonator.
 9. The method of claim 8 wherein said material to be treated is a dielectric sheet, and wherein the sheet is passed through said resonator with the plane of the sheet substantially parallel to the electric field vector of the traveling wave energy within the resonator. 